Otitis externa is certainly one of the most common problems seen in clinical practice. This topic has been divided in two lectures. Understanding the normal anatomy and physiology of the ear is important for the successful treatment of otitis cases. Therefore, in the first lecture, we will review the anatomy and physiology of the normal ear canal and we will talk about the pathophysiology associated with otitis externa. We will consider the primary and secondary causes, and predisposing and perpetuating factors leading to otitis. Finally, we will conclude with recommendations for the diagnostic approach of these cases, especially focusing on chronic, and recurrent, otitis externa.